The present applicant has provided several kinds of bolt or nut tightening devices comprising a tightening socket and a reaction force receiving member, the socket being rotatingly drivable by a motor and reduction means which are incorporated in the device (see, for example, JP-A No. 7-88777 and JP-A No. 8-197345).
With these tightening devices, the reaction force receiving member is brought into contact with a nut or like projection positioned in the vicinity of the nut to be tightened up for the projection to receive the reaction force of tightening.
Conventional tightening devices having a reaction force receiving member are used for bolts and nuts having a large nominal diameter, and the devices are large-sized.
Bolt and nuts having a small nominal diameter can be tightened up at a high speed by impact wrenches, which are therefore efficient to use. However, impact wrenches have the problem of releasing a loud noise during operation and impairing the work environment.
Accordingly, the applicant has made efforts to develop compact tightening devices having a reaction force receiving member for use with bolts and nuts of small nominal diameter, whereas provision of small tightening devices encounters the following problem.
When a nut is completely tightened up by the tightening device having a reaction force receiving member, the receiving member, as positioned between the tightened-up nut and a projection receiving the reaction force, performs a propping action with a great force in the direction of rotation of the tightening socket, and the device including the reaction force receiving member elastically deforms although slightly, regardless of whether the device is large-sized or small. Further even if the motor is deenergized after the completion of tightening, the motor rotates through inertia, exerting a force to hold the device elastically deformed.
The large tightening device has high rigidity in its entirety including the reaction force receiving member and therefore elastically restores itself effectively. Accordingly, if the motor is deenergized after the completion of tightening, the tightening device including the reaction force receiving member elastically restores itself, and the propping action of the receiving member as positioned between the tightened-up nut and the projection will be nullified automatically. Consequently, the tightening socket is smoothly removable from the nut.
However, small tightening devices are smaller than large tightening devices in rigidity and therefore restore themselves less effectively. Even if the motor is deenergized after the completion of tightening, therefore, the tightening device including the reaction force receiving member remains elastically deformed. Since the reaction force receiving member remains propping toward the direction of rotation as positioned between the tightened-up nut and the projection, great resistance acts against the removal of the tightening socket from the nut.
For this reason, the device can not be removed from the bolt and nut even if pulled straight axially of the bolt and nut.
The tightening device must be forcibly removed, as inclined with respect to the axis of the bolt and nut, from the bolt and nut.
With tightening devices having a reversely rotating function (loosening function), a forward-reverse changeover switch is manipulated for the motor, and the operation switch (trigger) is then pulled to reversely rotate the motor for a short period of time to nullify the propping action of the reaction force receiving member.
The former case requires labor and is inefficient.
In the latter case, the motor needs to be reversely rotated only for a moment to free the tightening device from elastic deformation, whereas it is difficult to properly pull the operation switch, with the result that the motor is likely to be reversely rotated to such an extent as to loosen the nut. Furthermore, it is necessary to manipulate the forward-reverse changeover switch first and then the operation switch, hence a cumbersome and inefficient procedure. In either case, such devices are not actually usable for tightening up many bolts and nuts at the site of construction.
An object of the present invention is to a small-sized tightening device which has a tightening socket and a reaction force receiving member, the socket being readily removable from the bolt or nut as completely tightened up although the device is compacted.